E-guns are used for various applications, and particularly for vapor deposition processes inside a sealed vacuum chamber. Such E-guns typically include an electron emitting source (emitter) for emitting a stream of electrons, high voltage leads to operate the emitter, a crucible for holding evaporant material, and a magnet for creating a magnetic field that directs the stream of electrons from the emitter onto the surface of the evaporant material. The incident electron stream evaporates the material to fill the chamber with a gaseous cloud for deposition onto substrates positioned in the chamber. U.S. Pat. Nos. 3,710,072 and 5,111,022 show various details of prior art E-guns.
One problem with such E-guns is arcing that occurs during operation, especially as the pressure inside the sealed vacuum chamber increases. More specifically, as the material in the crucible evaporates, a portion of it decomposes to positive ions plus some gas. These positive ions are emitted with a certain kinetic energy into the magnetic field, which guides the ions back toward the emitter along a similar path taken by the electron stream. Some of these ions can enter and damage the emitter.
Another problem caused by the positive ions in the chamber involves the high voltage leads, which extend from the chamber wall to the E-gun. These leads are typically bare high voltage conductors. Positive ions floating in the chamber between these conductors can cause arcing between the conductors and ground. Minimizing sharp corners on the conductors does not completely solve this arcing problem. Further, it is difficult to electrically insulate these leads because most insulating materials cannot withstand the high chamber temperatures that exist during vapor deposition.
One solution is proposed in U.S. Pat. No. 5,216,690 (issued to Hanks), in which a shield is added that surrounds all of the high voltage surfaces. The shield is grounded, and spaced from the HV surfaces by a distance that is below the mean free path of electrons at the highest pressure anticipated. The electrons making the transit, although accelerating quickly going from -KV cathode surface to nearby ground, have minimal ion collision probability over the entire distance. The electrons merely transfer to ground a minimal amount of energy. This suppresses arc-downs and glow discharges. However, the drawback to this type of e-gun is that the rigid ground shielded high voltage leads make it extremely difficult to install the device.
There is a need for an arc-free electron E-gun for vapor deposition processes.